View Full Version : Speedo Cable Leaks

Daniel Scully
05-21-2017, 09:07 PM
The speedo drive gear housing has a O ring that leaks but the inner seal is often over looked and seals the drive gear shaft thru the speedo housing. Seller on Ebay has a nice kit and is available elsewhere .


John ED Renstrom
05-21-2017, 11:18 PM
I see it only works for the bigger gears. as I recall there are two different sets of sleeves for that transmission. for some reason the 29 tooth gear is stuck in my head as being the correct one for teh 235 tires. but it might be that the 29 is the one for the 890s and you need to go 2 teeth bigger for the 235s.which means you need a bigger adapter also.

Paul Steinberg
05-22-2017, 12:10 AM
The speedometer cable doesn't care what gear set that you have inside of the transmission. The cable nut will fit any gear ratio of the vehicle, UNLESS the transmission was changed to a later or earlier transmission, and the speedometer drive gear mechanism is larger or smaller than that of the original transmission. If a transmission swap was made, putting a 1990's transmission into a 1960's car, then I wouldn't expect the 1960's speedometer cable to mount to a 1990's transmission.

John ED Renstrom
05-22-2017, 11:55 AM
On the th400 the gear that drives the cable is placed in a sleeve that it held to the case with a clamp. These o rings will seal that sleeve in the case. There are two different sleeves due to the spacing of the gears agents the drive gear in the transmission. In thinking this one threw I don't see his statement that this would not go on the smaller numbers as strange the outer shape of Either would be the same

John ED Renstrom
05-22-2017, 04:05 PM
just to fallow up here are the speedometer gear housing I have for the th-400.

I have one older housing that will fit all the gears of that style with a steel shaft

the plastic one has different dimanter shafts. that is why this kit if for the bigger numbers as the inside seal would be different the outer O ring is the same. the big blue tube is the inside gear that drives the out gear. the housing space the different tooth gears at the right spacing. lower numbers closer and higher numbers father away. with the different size shaft so that you don't get the wrong gear. if your sped o-meter is reading fast you go to a bigger number of teeth to slow it down and vice verse. the other adapter is as I recall for the truck with 20 in wheels. now then this is only for the transmission list in that add and for us we only think of the th-400. as that is what is in the pro cars from 64 to 76. others you do have to pull the tail stock to chant the drive gear inside. me I'm not a tyranny man just a few lesson learned on a 73 suburban I want the 16.5 tires off from

Daniel Scully
05-26-2017, 03:07 AM
This pic you can see where the drive stem comes thru and seals, this small inner seal is a cause of lots of leaks. The speed cable will sometimes carrier the trans fluidl all the way to the speedo head.

Joe Rackov
05-26-2017, 08:54 AM
Also,the housing where the gear shaft rides in may be worn also. Deep scoring or worn oval, both those conditions make sealing difficult. Not as prevalent on TH 400 transmissions as TH 350's with the die cast speedometer "bullet" style, not a factor on the steel ones.

I feel that the 400's lesser wear is that they were designed with a offset for the gear placement while 350's were a one size fits all, pressure and alignment.